System for Controlling Combustion Air

ABSTRACT

The object of the invention is to provide a system for controlling combustion air supply, in which the air supply to the primary and secondary air supply can be infinitely variable. The object is also to enable said system to be retrofitted in furnaces having a primary and a secondary air supply. To achieve this, a housing ( 1 ) having an internal, pot-shaped insert ( 5 ) provided with radial openings ( 9; 10 ) associated with either the primary air supply ( 7 ) or the secondary air supply ( 8 ) of the furnace is located between the furnace and the supply line for the combustion air, the cross-sections of said openings being infinitely variable via a pivotally mounted ( 17 ) motion link, the rotary angle of which is restricted by one or more stops ( 19 ). The motion link ( 17 ) is actuated by means of a drive unit ( 13 ) which in turn can be controlled by a control unit ( 23 ).

TECHNICAL FIELD OF THE INVENTION

The invention relates to a system for controlling the combustion airsupply in a solid fuel furnace with a primary air supply and a secondaryair supply according to the preamble to claim 1.

PRIOR ART

In wood or coal-burning solid fuel furnaces the air required forcombustion is usually supplied by a primary air supply and a secondaryair supply. In such a case, the primary air required for heating up andfor the combustion of coal is supplied to the furnace's combustionchamber in the lower area, i.e. through the grate. On the other hand,during the combustion of wood the combustion air is supplied into theupper area of the combustion chamber only via the secondary air supplyfollowing the heating up phase in which the combustion air is suppliedvia the primary air supply and secondary air supply.

Usually, the primary air supply and secondary air supply are setmanually. The disadvantage of this control method, however, is thatsettings can only be made by trial and error and by making estimates. Inaddition, making settings in this way is very time-consuming ascorrections have to be repeatedly made depending on the state ofcombustion.

Optimum combustion cannot therefore be achieved. Very many differenttypes of systems for controlling the air supply have therefore sincebeen developed to optimize the combustion of solid fuels such as wood orcoal.

For example, a solid fuel furnace is known from DE 20 2010 003 329 U1which has a regulating device for the primary air supply and aregulating device for the secondary air supply, both of which can beactivated by a linkage which is coupled to an adjusting device.

The disadvantage of this solution is that the regulating device, andtherefore the solid fuel furnace as well, is costly and complicated toconstruct.

A chimney furnace is described in EP 2 221 534 A2 with a control devicefor the air supply. To set the volume of the primary air supply andsecondary air supply the respective air ducts leading into thecombustion chamber are closed to a greater or lesser extent by means ofa rotatable control disk in which geometrically different openings arearranged.

Apart from the fact that this embodiment too is very costly andcomplicated to construct, it has the further disadvantage that thevolumes of air flowing through it can be set only in steps over thecross section created by the geometrically different openings in thecontrol disc.

A further means of controlling the combustion air supply into thecombustion chamber of a furnace via the primary or secondary air supplyis presented in EP 2 096 356 A2. This solution requires only one controlmechanism, comprising a temperature sensor and a flow regulator.However, the embodiment requires its own valve mechanism for the primaryair supply and its own valve mechanism for the secondary air supply. Inaddition, the embodiment also has separate shut-off elements which mustbe activated independently of the control mechanism in order to closethe air supply that is not required.

Despite the inherent simplicity of its design made possible because onlyone control mechanism is required, the embodiment is still very costlyto construct.

The principal reason why all these systems listed above for controllingthe air supply are costly and complicated to manufacture is that theyare combined with the furnace. An associated additional disadvantage ofall the embodiments previously referred to is that they cannot beretrofitted.

STATEMENT OF THE INVENTION

The present invention addresses the problem of developing a system forcontrolling the combustion air supply to a solid fuel furnace with aprimary air supply and a secondary air supply in which the supply of airto the primary or secondary air supply is to be controlled in aninfinitely variable manner. Its structure and manufacture are to be assimple as possible and the system is to be capable of being retrofittedin furnaces with a primary and secondary air supply.

The problem is solved according to the invention in that a housing isarranged between furnace and combustion air supply line, said housinghaving an internal, pot-shaped insert which is provided with radialopenings which are assigned either to the furnace's primary air supplyor secondary air supply, and whose cross sections are infinitelyvariable by means of a pivotally mounted motion link whose rotary angleis restricted by one or a plurality of stops, wherein the motion linkcan be actuated by means of a drive unit which can in turn be controlledby a control unit.

A solution has therefore been found which overcomes the disadvantages ofthe prior art referred to above. The use of a motion link provides avery simple solution which does not require additional mechanicaladjusting devices such as valves, rods and the like.

The structure of the furnace is simplified and, at the same time, theneed for an additional large installation space in the furnace iseliminated because it no longer has to accommodate complicated controlcomponents

A possible advantageous embodiment of the invention is set out in theother claim. The openings located in the housing which are normallyclosed and which can function as a bypass enable additional air to besupplied, if required, into the primary air supply and/or secondary airsupply, by bypassing the system for controlling the combustion airsupply. This ensures that there is always a minimum chimney draft toavoid the danger of the accumulation of dangerous gases.

EXECUTION EXAMPLE

An exemplary embodiment of a system for controlling the combustion airsupply according to the invention is described in detail below by meansof an execution example. The diagrams show the following details:

FIG. 1 a perspective view of the inlet side of a system according to theinvention for controlling the combustion air supply,

FIG. 2 a perspective view of the outlet side of a system according tothe invention for controlling the combustion air supply,

FIG. 3 a view of a system according to the invention for controlling thecombustion air supply,

FIG. 4 a section A-A from FIG. 3 in the closed position of the systemfor controlling the combustion air supply,

FIG. 5 a section B-B from FIG. 3 in the open position of the system forcontrolling the combustion air supply,

FIG. 6 a section A-A from FIG. 3 during the control of the combustionair supply of the primary air supply

FIG. 7 a section A-A from FIG. 3 during the control of the combustionair supply of the secondary air supply.

As can be seen in FIGS. 1 and 3, the system according to the inventionfor controlling the combustion air supply comprises a housing 1 fittedon the inlet side with a collar 2 which provides a means ofaccommodating a flexible air hose (not illustrated) for supplying theair required for combustion, if this is not to be removed from theinstallation space. A basket-shaped attachment 11 fastened in a fixedposition, for example by means of a bayonet lock 12, is located on theinlet side of the housing 1. A drive unit 13, described in detail below,is arranged in the interior of the attachment 11 (FIG. 5). The airrequired for combustion can flow through slit 14 through the housing 1in the direction indicated by a directional arrow.

On its outlet side the housing 1 has a flange 4 by means of which thesystem for controlling the combustion air supply can be connected to afurnace which is also not illustrated and which is suitable for thecombustion of solid fuels such as wood and/or coal and which has forthis purpose a divided inlet for the combustion air supply, in thisexecution example an inlet divided into a primary air supply on one sideand a secondary air supply on the other side.

In the housing 1 there is a pot-shaped insert 5 which is opened to theinlet side of the housing 1 and, in addition, separates the inlet sidefrom the outlet side (FIG. 2). In manufacturing this as a plasticcomponent it has proved to be advantageous, as shown in this executionexample, to construct housing 1 and insert 5 as a single piece. Theinner wall of the housing 1 is connected to the outer wall of the insert5 by intermediate webs 6, thereby continuing in the housing 1 thedivision of the combustion air supply existing at the inlet of thefurnace into a primary air supply 7 on one side and a secondary airsupply 8 on the other side. The inlet side of the housing 1 isfluidically connected to the primary air supply 7 on the outlet side bymeans of an opening 9 located in the circumferential area of the insert5 and is fluidically connected to the secondary air supply 8 on theoutlet side by means of an opening 10, also located in thecircumferential area of the insert.

The base of the pot-shaped insert 5 has in its center a bore which hasbeen designed as a bearing 15 for an axle which serves as a fulcrum fora motion link 17 attached to it. As can be clearly seen from FIGS. 4 and5 the radius of the motion link 17 has been determined such that theexterior circumferential area of the motion link 17 slides on the innerwall of the insert 5.

At the same time the arc length of the circumferential area of themotion link 17 is dimensioned such that the two openings 9 and 10 can becompletely covered on the one hand (FIG. 4), but also almost completelyopened on the other hand (FIG. 5). The pivoting range of the motion link17 required for this operation is defined by a rib 18 located on theinternal side of the motion link 17 and a stop 19 located on theattachment 11,

The drive unit 13, which has already been referred to above and which isattached in the interior of the attachment 11, serves to bring themotion link 17 into the required position. A rotary motion is generatedin the drive unit and transmitted to a driver 20 which is arrangedcentrally to the axle 16 and which incorporates a counterpart 21 locatedon the axle 16 to enable the motion link 17 to be pivoted into therequired position.

An electronic control unit 23, which in this execution example isattached by means of a holder 22 to the housing 1, controls the driveunit 13 by means of a cable which has not been depicted for the sake ofclarity, with control effected on the basis of data determined bysensors and processed in the electronic control unit 23. In this casethe sensors comprise, for example, a door contact switch, a sensor forrecording the temperature of the furnace body and a flue gas temperaturesensor.

In addition, in this execution example the system according to theinvention for controlling the combustion air supply enables additionalair to be supplied to the primary air supply and/or the secondary airsupply by bypassing the controlled air supply. To that end the flange 4,as can be seen in FIG. 5, has a plurality of closed openings 24 in thearea of the primary air supply 7 and the secondary air supply 8 whichmust be opened in varying numbers and assignments dependent on thedesign of the furnace to which the flange is connected. Where plastic isused as a material, this component can be conveniently manufactured, asdescribed above, in the form of a thin plastic layer with re-closablepredetermined breaking points. If necessary, the openings 24 can, forexample, be re-closed by stoppers that are not illustrated.

The system according to the invention for controlling the combustion airsupply described in this execution example has the following mode ofoperation:

In FIG. 4 the system for controlling the combustion air supply is shownin the closed position, i.e. in standby mode. The heating up phasebegins as soon as the furnace is filled with the selected fuel, anoperation signaled by the door contact switch. The motion link 17 ispivoted so far that both openings 9 and 10 are opened by the electroniccontrol unit 23 by means of the drive unit 13 as shown in FIG. 5.

The control phase begins on completion of the heating-up phase, usuallydefined as a minimum as the attainment of a specific flue gastemperature and furnace body temperature.

If coal is used as a fuel, the combustion air supply of the primary airsupply 7 is controlled. The motion link 17 is pivoted so far that theopening cross section of the opening 9 for the primary air supply 7 isopened and the opening 10 for the secondary air supply 9 is closed (FIG.6). This ensures that the opening 10 for the secondary air supply 8remains closed by the motion link 17, even when the opening crosssection of the primary air supply 7 changes when the positions of themotion link 17 change during the control process.

By contrast, if wood is used as a fuel, the combustion air supply of thesecondary air supply 8 is controlled. The motion link 17 is pivoted sofar that the opening cross section of the opening 10 for the secondaryair supply 8 is opened and the opening 9 for the primary air supply 7 isclosed (FIG. 7). It goes without saying that the system ensures in thiscase too that the opening 9 for the primary air supply 7 remains closedby the motion link 17 when the opening cross section of the secondaryair supply 8 changes because of the changing positions of the motionlink 17 during the control process.

On completion of the control phase the system for controlling thecombustion air supply assumes the standby mode shown in FIG. 4. Bothopenings 9 and 10 are closed by the motion link 17.

LIST OF REFERENCE NUMERALS

-   1 Housing-   2 Collar-   3 Directional arrow-   4 Flange-   5 Insert-   6 Intermediate web-   7 Primary air supply-   8 Secondary air supply-   9 Opening (primary air)-   10 Opening (secondary air)-   11 Attachment-   12 Bayonet lock-   13 Drive unit-   14 Slot-   15 Bearing-   16 Axle-   17 Motion link-   18 Rib-   19 Stop-   20 Driver-   21 Counterpart-   22 Holder-   23 Control unit-   24 Opening

What is claimed is:
 1. System for controlling the combustion air supplyin a solid fuel furnace which has a primary air supply and a secondaryair supply which are connected to an air supply line characterized inthat a housing (1) is arranged between said furnace and said air supplyline that has an internal pot-shaped insert (5) that is provided withradial openings (9; 10) which are assigned either to the primary airsupply (7) or the secondary air supply (8) of the furnace and whosecross sections are infinitely variable by means of a pivotally mountedmotion link (17), whose rotary angle is restricted by one or a pluralityof stops (19), wherein the motion link (17) can be actuated by means ofa drive unit (13) which can in turn be controlled by a control unit(23).
 2. System for controlling the combustion air supply according toclaim 1, characterized in that closable openings (24) are located in thehousing (1) for a defined addition of additional air into the primaryair supply (7) and/or the secondary air supply (8).
 3. A controller forcombustion air supply in a solid fuel furnace having a primary airsupply and a secondary air supply connected to an air supply line,comprising: a housing disposed between said furnace and said air supplyline, including an internal insert provided with openings assigned tosaid primary air supply and openings assigned to said secondary airsupply; a control unit; a drive unit controlled by said control unit andconnected to a motion link disposed to infinitely vary thecross-sections of said openings; and a plurality of stops disposed torestrict the rotary angle of said motion link.
 4. A claim in accordancewith claim 3, further comprising that said openings are radial openingsprovided in said housing.
 5. A claim in accordance with claim 3, whereinsaid internal insert is pot-shaped (5).
 6. A claim in accordance withclaim 3, wherein the radial openings (9; 10) which are assigned eitherto the primary air supply (7) or the secondary air supply (8) of thefurnace and whose cross sections are infinitely variable.